1. Field of the Invention
The present invention relates to a magnetic recording medium such as a magnetic disc having a low friction coefficient and an excellent durability.
2. Discussion of Background
The magnetic disc for use in external memories for computer or the like require a shortened distance between the magnetic disc and the magnetic head, i.e., a decreased floating height of the magnetic head to provide a higher reproduction output. For this purpose, the surface of the magnetic disc is preferably smooth. However, when the surface of the magnetic disc is too smooth, the magnetic head may stick to the magnetic disc, thereby causing damage to the magnetic disc or the magnetic head. Therefore, the substrate is subjected to a texture treatment to provide an appropriate surface roughness.
As the texture treatment, there have been heretofore proposed several methods. For example, a mechanical polishing process has been proposed for aluminum substrates. For glass substrates, a chemical etching process (JP-A-64-37718 (The term "JP-A" as used herein means an "unexamined published Japanese patent application")) and the application of a particle-containing coating (JP-A-1-194128), have been proposed. For carbon substrates, thermal oxidation (JP-A-4-214225) has been proposed. However, these methods are insufficient to meet current requirements for further decreasing the floating height of the magnetic head.
A texture treatment which can further decrease the floating height of the magnetic head, while maintaining excellent durability is needed, i.e., a surface that has both an appropriate roughness, and a sufficient smoothness.
A variety of techniques meeting these demands have been proposed. Examples include a method which comprises the vacuum evaporation of a low melting metal such as Sn and In to form an unevenness (as disclosed in JP-A-60-211614, JP-A-61-240429), a method which comprises sputtering of low melting metal such as Al and Cu to form a discontinuous islands (as disclosed in JP-A-3-73419), and a method which comprises using high melting metals such as Cr, Mo and W, to form a roughened surface (as disclosed in JP-A-2-267722).
These methods have the advantage in that texture treatment and formation of a magnetic layer can be carried out in a vacuum system consecutively. However, these methods have some disadvantages. For example, if a single low melting metal is used, the resulting unevenness has poor roughness, and is peelable due to a poor adhesivity to the substrate, rendering its use impractical. Further, if a high melting metal is used, the resulting unevenness has poor roughness and poor durability (CSS properties).